The German patent publication 4,231,578A1 discloses a method for determining the structural strength of tires, in the case of which coherent light is shone onto the tire, the radiation reflected by the tire is split up into two beams parts in a dual beam interferometer, in the dual beam interferometer one of the two beam parts is tilted in relation to the other beam part (shearing), in the dual beam interferometer one of the two parts of the radiation is incrementally shifted in phase, a component representing the radiation due to reflectance from the test object, which is split into two beam parts, is recombined in the dual beam interferometer by components forming an image of the surface of the tire with a large aperture, to an electronic image sensor system and the signals at the output of the image sensor system are digitalized and further processed in an image processing system to give a modulo-2.pi. image, and the modulo-2.pi. image is confirmed as an output gray value image.
In accordance with the German patent publication 19,502,073 A1 the above mentioned method is further developed by so partially differentiating the output gray value image that a second gray value image is produced, identical to the output gray value image and same is geometrically displaced in relation to the output gray value image in the shearing direction and is modified by a gray value, which is constant over the entire image range and the second gray value image, manipulated in this manner, is subtracted from the output gray value image so that a resulting gray value image is produced, on which any defects in the tire, which may be present, can be recognized.
When it is considered that structural damage in car tires, more particularly in the carcass including the belt, may substantially reduce the safety of driving the motor vehicle, it will be seen to be desirable to perform a tire check at regular intervals.
In U.S. patent application Ser. No. 09/094,143, which is incorporated herein by reference, there is a proposal for checking a tire by mounting the wheel, which bears the tire to be checked, on a wheel balancing machine and moving a test head up to the tire to be at a predetermined check distance for producing an interferogram. Checking for defects is performed on a first segment of the tire. Then the wheel is rotated further by the balancing machine by an amount equal to a checked segment and the last-mentioned steps are repeated until the entire tire has been checked. The tire testing device accordingly comprises a balancing machine, on which the wheel bearing the tire to be checked is mounted, a positioning means for a test head, with which the test head may be moved up to the tire as far as a predetermined check or test distance for producing an interferogram, and a control means for the balancing machine in order to rotate the wheel by an amount equal to one check segment.
In U.S. patent application Ser. No. 09/093,890, which is incorporated herein by reference, there is a proposal for checking a tire by mounting the wheel, which bears the tire to be checked, on a driven roller set. The tire checking comprises an air pressure means for changing the tire pressure and furthermore a testing head and a computer. Furthermore the apparatus comprises at least one driven roller set, onto which the motor vehicle with the wheel, which bears the tire to be checked, is to be driven, a positioning means for the test head, with which the test head can be moved toward the tire to be at a predetermined distance therefrom for producing interferograms and a control means for the roller set in order to rotate same an amount equal to the size of a check segment, when checking of the preceding segment has been completed.